Intense Light Irradiation Research Articles

Characteristics of carbonaceous aerosols in ambient PM2.5 during the COVID-19 period in Nanjing

In order to explore the variations of carbon components[including organic carbon (OC) and element carbon (EC)] in PM2.5 at the urban area of Nanjing during the breakout of COVID-19 period, PM2.5, OC and EC mass concentrations were measured by online monitoring from January to February 2020. Compared to the concentrations before the emergency response, the PM2.5 concentration after the emergency response was reduced by 41.2% and EC reduced by 57.9%. These results indicate that the shutdown significantly reduced PM2.5 and EC concentrations, but the OC concentration increased. Before the emergency response, the OC and EC concentrations were low in daytime and high at night and early morning. After the emergency response, the average concentration of EC only had a slight change within a day and maintained at low concentration level, OC showed a curve trend which was higher in the afternoon and lower in morning and evening. The significant decrease of PM2.5 concentration after the emergency response period led to the increasing of light radiation intensity, which promoted the formation of secondary organic carbon (SOC). The SOC concentration increased when the PM2.5 and EC concentrations decreased, and the correlation between OC and EC also decreased significantly. © 2021, China Environmental Science Press. All rights reserved.

Comparative Analysis of Solar Cell Efficiency between Monocrystalline and Polycrystalline

The output power capacity of solar panels depends on the intensity of light radiation it receives, while the life time depends on the high and low temperatures experienced. The purpose of this study was to examine the effect of light intensity on the output power and efficiency of solar panels. This study applies a direct measurement method using a monocrystalline type solar panel and a polycrystalline type with the same power capacity with a peak capacity of 50 Wp. The research was conducted indoors using lights as light sources by varying the light intensity in the range 2.21-331.01 W/m2 with a distance of 50 cm from the light source from the solar panel. The increase in temperature on the surface of the solar panel can also reduce the power capacity generated, and the monocrystalline type is more resistant to temperature increases than polycrystalline. The efficiency of the solar panel changes when given light with a certain energy, up to the highest intensity of 331.01 W/ m2, with the highest temperature that occurs resulting in an efficiency of 12.84% on the Monocrystalline Panel and 11.95% on the Polycrystalline Panel.

Spatial Identification of Housing Vacancy in China

The housing vacancy rate (HVR) is an important index in assessing the healthiness of residential real estate market. In China, it is hardly to take advantage of the basic data of real estate information due to the opaque of those data. In this paper, the HVR is estimated to two scales. At the grid level, urban area ratio was calculated by nighttime images after eliminating outliers of nighttime images and night light intensity of non-residential pixels in mixed pixels by a proposed modified optimal threshold method, and built-up areas in each pixel were extracted from the land-cover data. Then, the HVR is calculated by comparing the light intensity of specific grid with the light intensity of full occupancy rate regions. At the administrative scale, the GCI (‘ghost city’ index) is constructed by calculating the ratio of the total light radiation intensity of a city to the total construction land area of the city. The overall spatial differentiation pattern of the vacant houses in the national prefecture level administrative regions is analyzed. The following conclusions were drawn: vacant housing is rare in certain eastern coastal cities and regions in China with relatively fast economic development. Cities based on exhausted resources, some mountainous cities, and cities with relatively backward economic development more typically showed high levels of housing vacancy. The GCI of prefecture-level administrative units gradually declined from north to south, whereas the east-west distribution showed a parabolic shape. As city level decreased, the GCI registered a gradual upward trend. China’s urban housing vacancy can be divided into five categories: industry or resources driven, government planned, epitaxy expansionary, environmental constraint and speculative activate by combining the spatial distribution of housing vacancy with the factors of natural environment, social economic development level, and population density into consideration.

Effects of intense pulsed light and gamma irradiation on Bacillus cereus spores in mesquite pod flour

This study was conducted to evaluate the inactivation of Bacillus cereus spore in mesquite flour with intense pulsed light (IPL) and gamma radiation. The physical, chemical, and toxicity of treated mesquite flour were also investigated. The results showed that up to 3.51 log10CFU/g B. cereus spore inactivation was achieved with 8 kGy of gamma radiation, and up to 1.69 log10CFU/g reductions could be achieved after 28s of catalytic IPL exposure. Although chemometric analysis showed 9-hydroxy-10,12-octadecadienoic acid was slightly increased after a 28s-catalytic IPL treatment, the concentration is within the acceptable range. No significant increase in acetic or propionic acids (typical off-flavor volatile compounds) was observed after either treatment. For cytotoxicity, the Caco-2 cell viability analysis revealed that these two technologies did not induce significant cytotoxicity to the treated mesquite flour. Overall, these two technologies exhibit strong potential for the decontamination of B. cereus in mesquite flour.

A model for photothermal conversion of graphene-filled nanocomposites under NIR irradiation

Graphene, acted as an excellent photothermal inorganic filler in photothermal smart composites, has triggered the fast increasing research upsurge in biomedical imaging, photothermal therapy, photothermal driving and so on recently. Many studies have shown that a low mass loading graphene nanosheets (GNSs) in a matrix can provide the nanocomposite with high photothermal conversion efficiency in the near-infrared (NIR) region due to its strong NIR adsorption and high thermal conductivity. Aiming to indicate the photothermal conversion mechanism, we present an analytical approach based on the Maxwell electromagnetic wave theory, thermodynamics method and effective medium approximation. The influence mechanism of graphene concentration and size, light intensity of NIR irradiation, interfacial thermal resistance between graphene and matrix on the photothermal conversion are all explained in this paper.

Self-Suspended Photothermal Microreactor for Water Desalination and Integrated Volatile Organic Compound Removal.

Steam generation and photocatalytic degradation of organic pollutants based on solar light are regarded as two important strategies for addressing the water scarcity issues. The water evaporation efficiency was greatly inhibited by the high cost, low stability, and low efficiencies of solar light absorption and photothermal conversion of photothermal materials. Moreover, volatile organic compounds (VOCs) are easily volatilized and enriched in as-distilled water during the photothermal process. Inspired by the structure of biomass materials in nature, a bifunctional solar light-driven steam generation and VOC removal microreactor was explored by coating commercial TiO2 (P25) powders on a carbonized biomass waste Flammulina. With the 3D aligned porous carbon architectures, this microreactor exhibited both a high water evaporation rate (37.0 kg m-2 h-1) and a high energy conversion efficiency (91.2%) under simulated sunlight irradiation (light intensity = 25.5 kW m-2). A high VOC removal rate (80.9% in 40 min) was also achieved during the steam generation process via choosing phenol as the probe pollutant molecules. The nature-inspired designing concept and bifunctional microreactor in this study may open up a new strategy for producing clean distilled water from seawater with an efficient removal of VOCs.

Effect of excessive Cs and O on activation of GaAs(100) surface: From experiment to theory

The surface Cs–O activation process directly determines quantum efficiency and stability of negative-electron-affinity photocathodes. To investigate the effects of excessive Cs and O supply on activation and to explore a more effective Cs–O activation recipe, Cs–O activation experiments of GaAs(100) photocathodes are carried out based on the current-driven solid Cs and O dispensers. By a comparison of differences in activation photocurrent, quantum efficiency, and photocurrent decay, it is found that the recipe of excessive O and non-excessive Cs is not suitable for activating GaAs photocathodes, while the recipe of continuous and completely excessive Cs along with intermittent and non-excessive O can achieve the most excellent photoemission performance, including the highest quantum efficiency in the long-wave threshold region and best stability under intense light irradiation after activation. Furthermore, this improved activation recipe with the least Cs–O alternating cycles is easier to operate. Combined with density functional calculations and dipole layer model, it is found that the activation recipe of completely excessive Cs and non-excessive O can form effective dipoles to the greatest extent, and avoid the direct interaction between As atoms and O atoms to form As–O–Ga oxides on the GaAs(100) reconstructed surface.

Evaluation of the use of free or supported phenalenone based on natural halloysite for phenol photodegradation in aqueous solution

Our work has focused on evaluating the use of phenalenone (PN) for phenol photodegradation in aqueous solution. This evaluation was conducted using both free and supported (PN) on halloysite nanotubes (HNTs). The photodegradation study took place in an annular photoreactor with ultraviolet (UV) or visible irradiation, whose emission corresponded to PN absorption wavelength. The influence of operating parameters, namely pH, initial phenol and PN concentrations, light intensity, and type of irradiation (i.e. UV, visible), has been examined. Phenol photodegradation was performed in the presence of sodium azide, propan-2-ol and, lastly, nitrogen (N2) to determine the mechanism pathway. Results reveal pH as the most important parameter affecting phenol photodegradation. A complete phenol transformation could be attained within 120 min under UV irradiation and within 300 min under visible irradiation at pH 12. The PN/phenol ratio alters photodegradation kinetics, especially under UV irradiation. The photodegradation rate was higher with free PN than with a supported photosensitizer. Pseudo-first-order kinetics were observed under both UV and visible irradiation. A type II mechanism proved to be the main pathway in phenol photodegradation, with possible contribution from a type I mechanism.

Facile and fast preparation of Nano-rod ZnO for photocatalytic application under low intensity of UV light irradiation

Objective: This study aims to degrade the organic dyes in aqueous medium and low UV intensity by nano-rod ZnO. Methodology: The ZnO was prepared by a facile and fast method, as-synthesized ZnO was characterized by SEM,XRD, N2 adsorption/desorption isotherm, and diffuse reflectance UV-vis. The composition of samples before and after calcination steps was analyzed by XRD. The catalytic performance of ZnO was evaluated by the degradation of dyes in aqueous solution under a low UV light irradiation. Finding: the precursor was completely transformed to ZnO at 400 ◦C. The ZnO was nanorod structure with the crystalline phase of hexagonal wurtzite. The degradation efficiency of ZnO for Janus Green B in 10 min was 96.8%, it was 95.8% in 40 min for Congo Red. The reaction kinetic of photodegradation of dyes was followed by the first-order kinetic model and the photodegradation mechanism of ZnO for dyes was proposed. Application/Improvement: The facile and fast method was developed for the synthesis of nano-rod ZnO, it could be applied for practical application in wastewater treatment. Keywords: ZnO; dyes; photocatalyst; first-order kinetic; Nano-rod

Characterizing surface viscoelastic integrity of ultra-fast photo-polymerized composites: Methods development

ObjectiveResin-Composites are now available designed for polymerization using 3 s of intense light irradiation. The aim was to develop an experimental method to probe their surface viscoelastic integrity immediately following such rapid photo-cure via macroscopic surface indentation under constant stress as a function of time. MethodsTwo bulk-fill composites (Ivoclar AG) were studied: Tetric PowerFill (PFill) and PowerFlow (PFlow). Split molds were used to fabricate cylindrical {4 mm (dia) × 4 mm} paste specimens, irradiated at 23 °C at 0 mm from the top surface with a BluephasePowerCure LED-LCU, with 3 s or 5 s modes, emitting 3 and 2 W/cm2, respectively. Post-irradiation specimens were immediately transferred to an apparatus equipped with a flat-ended indentor of 1.5 mm diameter. 14 MPa compressive stress at the indentor tip was applied centrally in < 2 min and maintained constant for 2 h. Indentation (I) magnitudes were recorded in real-time (t), with I(t) data re-expressed as % indentation relative to the 4 mm specimen height. After 2 h, the indentor was unloaded and indentation recovery was monitored for a further 2 h. Parallel sets of measurements were made where indentation was delayed for 24 h. Further measurements were made with more conventional composites: EvoCeram Bulk Fill (ECeram) and Tetric EvoFlow Bulk Fill (EFlow). These were irradiated for 20 s at 1.2 W/cm2. Kinetic data were curve-fitted to exponential growth functions and key parameters analyzed by ANOVA and post-hoc tests (α = 0.05). ResultsI(t) plots looked initially similar to bulk creep/recovery: rapid deformation plus viscoelastic response; then, upon unloading: rapid (elastic) recovery followed by partial viscoelastic recovery. However, unlike multiply irradiated and stored bulk-creep specimens, the present specimens were exposed to only 3 or 5 s “occlusal” irradiation; generating “hard” surfaces. Subsequently, during the 2 h indentation, the polymer matrix network continued to harden and consolidate. Upon initial loading, I(t) reached 2–3% indentation, depending upon the formulation. Upon unloading at 2 h, elastic recovery was only ca. 1 %. Delayed loading for 24 h, generated I(t) plots of significantly reduced magnitude. Most importantly, however, the I(t) plots for ECeram and EFlow, after 20 s irradiation, showed I(t) magnitudes quite comparable to the PFill and PFlow rapid-cure composites. SignificanceMacroscopic indentation creep has been shown to be a workable procedure that can be applied to rapid-cure materials to assess their immediate surface integrity and developing viscoelastic characteristics. The applied stress of 14 MPa was relatively severe and the indentation/recovery profiles of PowerFill materials with only 3 or 5 s irradiation demonstrated comparability with their established 20 s cure siblings, evidencing the suitability of the PowerCure system for clinical application.

Acquisition, Maintenance, and Ecological Roles of Kleptoplasts in Planoglabratella opercularis (Foraminifera, Rhizaria)

Kleptoplasty or acquisition of chloroplasts from ingested photosynthetic organisms, is thought to be a key factor in determining the trophic requirements and carbon mineralization of foraminifera, consequently influencing their ecology, evolution, and calcification. However, the acquisition, maintenance, and functions of “stolen” chloroplasts (kleptoplasts) in foraminiferal cells have not been well characterized. Using molecular phylogeny and experimental measurements of oxygen flux and intracellular (vacuole) pH, we characterized aspects of kleptoplast origin and function in Planoglabratella opercularis (d’Orbigny), a rocky-shore benthic foraminifera. We determined that the kleptoplasts in P. opercularis are derived from various species of epiphytic diatoms. The acquisition of epiphytic diatoms is congruent with the behaviour of P. opercularis, which crawls on the thalli of coralline algae and grazes on the microalgae on the algal surface. Kleptoplasts were located near the host foraminiferal cell periphery, just under the pore plug, mainly along the dorsal side, which is important for oxygenic photosynthesis. The lifespan of kleptoplasts varied according to food availability and to the intensity and duration of light irradiation. Planoglabratella opercularis was able to capture not only diatom chloroplasts but also those from Chlorella. Kleptoplastids of diatom origin decreased in autofluorescence and were digested within 11 days under light in the absence of food. This suggests that host foraminifera frequently capture new diatoms to sustain kleptoplasts. Kleptoplastid autofluorescence was prolonged in the dark or 24:24-h light:dark cycle, and when food was available. Host foraminifera metabolized food to maintain the activity of kleptoplasts and effectively utilized photosynthetic products from both organic and inorganic materials in response to the ambient environment. This suggests that P. opercularis behaves as a mixotroph. Simultaneously, kleptoplasts maintain a high intracellular pH environment, indicating that foraminifera capture kleptoplasts not only to gain their photosynthates but also to control the intracellular pH levels to construct a high magnesian calcite test.

UV Light-Irradiated Photocatalytic Degradation of Coffee Processing Wastewater Using TiO2 as a Catalyst

The coffee industry generates a significant amount of wastewater that is rich in organic loads and is highly acidic. The present study investigates the potential of the heterogeneous photocatalytic oxidation process to reduce the pollutant load in coffee processing wastewater. The experimental runs were conducted to evaluate the effect of operative parameters such as pH, catalyst dosage, intensity of UV light irradiation, and addition of oxidant on Chemical Oxygen Demand (COD) and colour reduction. Significant results for COD and colour removal, 67%, and 70% respectively, were achieved at a pH of 4 with titanium dioxide (TiO2), and a catalyst dosage of 500 mg/L, using four ultraviolet-C (UV-C) lamps of 16 W each. With the addition of hydrogen peroxide (H2O2) as an oxidant, the removal efficiency increased to 84% and 75% for COD and colour, respectively. Finally, the best results obtained by photocatalytic degradation using UV light were compared to those using solar light. Based on the investigation, it was inferred that the pollutant removal efficiency in coffee pulping wastewater was also considerably high under sunlight. These findings may have relevance in terms of application in countries where coffee processing is carried out and where sunlight irradiance is usually strong: the technique could be exploited to decrease the pollutant content of this wastewater sustainably.

Phosphor-free, color-mixed, and efficient illuminant: Multi-chip packaged LEDs for optimizing blue light hazard and non-visual biological effects

Currently many evaluation models on the photobiological effects (PBE) of light sources do not consider the influence of age and luminance on the pupil diameter, which affects the light radiation intensity on the human retina. In this study, the pupil diameter is taken into consideration when evaluating the PBE of several light sources. Moreover, the correction factor M is proposed. The blue light hazard (BLH) efficacy and the circadian rhythm (CR) effects of the daylight at dusk, together with three indoor light sources with a correlated color temperature (CCT) of about 3000 K were evaluated by using a corrected evaluation model. The results show that an incandescent lamp is more photobiologically friendly for humans, despite being inefficient. Based on high wall-plug efficiency (WPE) GaN-based yellow (565 nm, 24.3%@20 A/cm2) and green (522 nm, 41.3%@20 A/cm2) LEDs on silicon substrate, incandescent-like spectrum and phosphor-free color-mixed white LEDs (CM-LEDs) with a general color rendering index (CRI) of 94, a CCT of 2866 K, and an efficiency of 131 lm/W were manufactured by mixing blue, cyan, green, yellow and red LEDs. The PBE evaluation results of such CM-LEDs are superior to those of an incandescent lamp. Moreover, blue light free and candlelight-toned LEDs with an efficiency of 120.3 lm/W, a general CRI of 84, a special CRI R9 of 93.3, and a CCT of 1810 K were fabricated by mixing yellow and red LEDs (R&Y-mixed LEDs). The R&Y-mixed LEDs show no blue light weighted quantities and have a weaker influence on the CR shift. They are photobiologically friendly for humans and suitable for nocturnal indoor and outdoor lighting environments.

Photo-Fenton disinfection at near neutral pH: Process, parameter optimization and recent advances

Abstract The photo-Fenton process is an advanced oxidation process that uses the hydroxyl radical to disinfect and decontaminate water. Its non-selectivity makes it ideal for the removal of a range of microorganisms including those with antimicrobial resistance. Optimum parameters such as pH, temperature, hydrogen peroxide and iron concentrations and the intensity and wavelength of light irradiation are important to carry out an efficient photo-Fenton process. Traditionally photo-Fenton has been carried out at low acidic pH to obtain greater efficiency, but recent studies have been performed at near neutral. The current review examines the effectiveness of the photo-Fenton process at a near neutral pH for the disinfection of water. The optimal pH was seen to be at 2.8, with the efficiency of the photo-Fenton process decreasing as the pH rises. The optimal reagent concentrations showed considerable variation depending on the iron catalyst used and the iron to hydrogen peroxide concentration used. The effect of irradiance and temperature showed improved efficiency with higher levels. Different types of microorganisms such as E. coli, Pseudomonas sp., Enterococcus faecalis, Klebsiella pneumonia, Salmonella spp., total Coliforms, MRSA, MSSA, B. subtilis, Clostridium sp., Faecal Coliform, MS2 coliphage and Curvularia sp. are also examined and the effect the process will have on them. The design of reactors, such as compound parabolic reactors are also examined. The impact of light sources, including the recent reports on LEDs, on the production of hydrogen peroxide and thereby the improvement in the overall photo-Fenton disinfection is also discussed in detail. Finally, a techno-economic analysis to explain various costs associated with photo-Fenton process has also been carried out. It is concluded that the development of new heterogeneous supported immobilised catalysts that could work at the near neutral pH is an area, which requires considerable future research.

Optical Defects Engineering of Metal Oxide Nanosheets Toward Exceptional Chemiresistor

Metal oxide nanosheets (NSs) exhibit intriguing physicochemical properties such as high specific surface area, high fraction of reaction sites, thus leading to promising performance in various applications including energy storage, catalysis, and gas sensing. [1] Beyond the 2D metal oxide NSs, defect engineering and/or control of non-stoichiometry, that is, control of metal or oxygen vacancies, are a few of the powerful strategies to generate abundant active sites to enhance gas sensing performance. [2] Precise control of the heat treatment, ramping rate control or reducing heat treatment as examples, is an effective way to generate the oxygen vacancies, but is time-consuming which requires high thermal-budget. Building-up of hetero-junctions is another powerful method to boost up the sensing performance. [3] However, it has been a challenge to prepare thin-layered heterogeneous metal oxide NSs with abundant active defect sites.An optical engineering to generate controllable oxygen vacancies and new crystal phases on various metal oxide nanosheets (NSs) is introduced via graphene oxide (GO) templating route followed by intense pulsed light (IPL) irradiation. Negatively charged GO flakes and metal ions readily self-assemble to form GO@M (where M = Sn2+, Co2+, Ti4+, and Zn2+) and polycrystalline metal oxide NSs, such as SnO2, Co3O4, TiO2, and ZnO, are successfully synthesized after calcination. Upon a few flashes of IPL irradiation (< 20 ms), a rapid increase in temperature (1200 °C) has induced evolution of defect sites and new crystal phases. As a representative, optically treated Pt-SnO2 NSs showed unparalleled formaldehyde (HCHO) response, excellent selectivity, low detection limit (100 ppb), and fast response speed (< 10 s) assisted by the synergistic effects of the Pt catalysts, numerous oxygen vacancies, and hetero-junctions formed by flash-induced partial reduction of n-type SnO2 to p-type SnO. This defects engineering method could greatly strengthen the design of various heterogeneous metal oxide NSs and their potential application toward various fields with the optimal customized physicochemical properties.

The surface plasmonic welding of silver nanowires via intense pulsed light irradiation combined with NIR for flexible transparent conductive films.

In this work, surface plasmonic welding of silver nanowires (AgNWs) by intense pulse light (IPL) combined with NIR was investigated. AgNWs were coated on a flexible PET (polyethylene terephthalate) substrate using a bar-coater. The coated AgNW films were welded at room temperature and under ambient conditions by white IPL from a xenon lamp, assisted with light from a UV-C (ultraviolet C) and NIR (near infra-red) lamp using an in-house multi-wavelength IPL welding system. In order to investigate the welding mechanism, in situ monitoring with a Wheatstone bridge electrical circuit was performed. The sheet resistance changes of AgNW films during the welding process were monitored under various IPL conditions (e.g. light energy and on-time) with and without UV-C and NIR light irradiation. The microstructure of the welded AgNW film and the interface between the AgNW film and the PET substrate were observed using a scanning electron microscope (SEM) and transmission electron microscope (TEM). COMSOL multi-physics simulations were conducted and compared with the in situ monitoring results to discuss the in-depth mechanism of the IPL welding of AgNWs and its dependence on the wavelength of light. From this study, the optimal IPL welding conditions and appropriate wavelength were suggested, and the optimized IPL welding process could produce AgNW film with a lower sheet resistance (45.2 Ω sq-1) and high transparency (96.65%) without damaging the PET substrate.

Comparison of electrical wire explosion characteristics of single wire and wire array in air

In this paper, discharge characteristics of a planar copper wire array explosion driven by a microsecond pulsed current source (500 J stored energy) in atmospheric air medium were studied. Meanwhile, controlled experiments were performed with single wire cases. With a 2 cm distance between electrodes, 2-16 copper wires with a diameter of 100 μm were selected to form planar copper wire arrays, and single copper wires with diameter of 50-400 μm were selected for comparisons. Load voltage, circuit current and light radiation intensity were measured. Electric power and deposited energy were calculated. The experimental results show that for the single wire case, with the increase of mass (diameter), the process of vaporization and ionization become slower, manifested as a delay of the voltage peak and an increase of the full width half maximum (FWHM) of the voltage pulse from 0.07 μs to 0.64 μs. In contrast, although the explosion time of wire array load was delayed with the increase of mass, the duration of vaporization and ionization did not change significantly with a FWHM of 0.11 ± 0.01 μs. In addition, the deposited energy of wire array load before breakdown was lower than that of single wire load with the same mass. As for the optical radiation intensity, under three cases with the same mass, the peak intensity of wire array explosion is about 28%, 49% and 52% higher than that of single wire explosion. There may be two reasons which cause the difference between the single wire load and wire array load. First, the larger specific surface area of the wire array load makes faster phase transitions. Second, the development of thermal or magnetohydrodynamics for the two kinds of loads was different, which should be responsible for the differences in energy deposition and optical emission.

Control of thermal deformation with photonic sintering of ultrathin nanowire transparent electrodes.

Development of electronic devices on ultrathin flexible plastic substrates is of great value in terms of portability, cost reduction, and mechanical flexibility. However, because thin plastic substrates with low heat capacity can be more easily damaged by thermal energy, their use is limited. Highly flexible nanowire (NW) transparent conductive electrodes on ultrathin (∼10 μm) low cost polyethylene terephthalate (PET) substrates are fabricated. The control of intense pulsed light (IPL) irradiation process parameters to induce NW welding for maximum conductivity and minimal thermal damage of the PET substrate is explored. For this purpose, trends in temperature variation of NW thin films irradiated by IPL under various operating conditions are numerically analyzed using commercial software. Simulations indicate that irradiating light operated at a higher voltage and for a shorter time, and use of multiple pulses of low frequency can reduce thermal deformation of the PET substrate. Furthermore, we experimentally confirm that NW transparent electrodes can be successfully fabricated with less thermal deformation of the ultrathin plastic substrate when light is irradiated under well-controlled conditions derived from the simulation. The highly flexible NW transparent conducting electrode exhibits excellent mechanical flexibility to withstand severe deformation and can be successfully implemented in flexible organic light-emitting diodes (OLEDs).

Design of Multi-Wavelength Optical Sensor Module for Depth-Dependent Photoplethysmography.

The multi-wavelength photoplethysmography sensors were introduced to measure depth-dependent blood volume based on that concept that the longer the light wavelength, the deeper the penetration depth near visible spectrum band. In this study, we propose an omnidirectional optical sensor module that can measure photoplethysmogram while using multiple wavelengths, and describe implementation detail. The developed sensor is manufactured by making a hole in a metal plate and mounting an LED therein, and it has four wavelength LEDs of blue (460 nm), green (530 nm), red (660 nm), and IR (940 nm), being arranged concentrically around a photodetector. Irradiation light intensity was measured by photoluminescent test, and photoplethymogram was measured with each wavelength simultaneously at a periphery of the human body such as fingertip, earlobe, toe, forehead, and wrist, in order to evaluate the developed sensor. As a result, the developed sensor module showed a linear increase of irradiating light intensity according to the number of LEDs increases, and pulsatile waveforms were observed at all four wavelengths in all measuring sites.

PHOTOTUNABLE SELECTIVE REFLECTION OF CHOLESTERIC LIQUID CRYSTALS

The dependence of the helical pitch of a cholesteric liquid crystal based on a composite photosensitive chiral dopant (cChD) on the intensity of light irradiation was studied. The transmission spectra and the selective reflection spectra of cholesteric liquid crystal cells were measured. The concentration of the cChD additive is calculated, so that the peak of selective reflection and its rearrangement occurs in the visible range of the electromagnetic radiation spectrum (380-780 nm). The possibility of photo-control by shifting the peak of the selective reflection of the cChD additive was studied, when exposed to LEDs with wavelengths of 365 nm and 450 nm, while reducing or increasing the intensity, a change in the spiral pitch was observed. Depending on the light intensity, part of the molecules of the chiral additive containing the azo group underwent isomerization, i.e. molecules in the trans-form passed to the cis-form, which led to a spectral shift of the selective reflection peak. If a small intensity of the 365 nm LED was applied, then some of the molecules were forced to transition from the trans- to the cis-form, and then, when illuminated with a 450 nm LED, from the cisto the trans-form. After reversible rearrangement, the properties of cholesteric liquid crystal changes due to interaction with light, because under the influence of light, the equilibrium ratio of the trans- and cis-isomers of the molecules of the substance changed, which macroscopically changed the torsion force of the chiral additive. Using two LEDs of 365 nm and 450 nm with different emission spectra, a reversible control of the cChD selective reflection peak in the visible range was obtained. The maximum displacement occurred at approximately 145 nm.